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CRISPR (clustered regularly interspaced short palindromic repeats) loci and their associated (cas) genes encode an adaptive immune system that protects prokaryotes from viral(1) and plasmid(2) invaders. Following viral (phage) infection, a small fraction of the prokaryotic cells are able to integrate a small sequence of the invader's genome into the CRISPR array(1). These sequences, known as spacers, are transcribed and processed into small CRISPR RNA guides(3-5) that associate with Cas nucleases to specify a viral target for destruction(6-9). Although CRISPR-cas loci are widely distributed throughout microbial genomes and often display hallmarks of horizontal gene transfer(10)(-12), the drivers of CRISPR dissemination remain unclear. Here, we show that spacers can recombine with phage target sequences to mediate a form of specialized transduction of CRISPR elements. Phage targets in phage 85, Phi NM1, Phi NM4 and Phi 12 can recombine with spacers in either chromosomal or plasmid-borne CRISPR loci in Staphylococcus, leading to either the transfer of CRISPR-adjacent genes or the propagation of acquired immunity to other bacteria in the population, respectively. Our data demonstrate that spacer sequences not only specify the targets of Cas nucleases but also can promote horizontal gene transfer.

A search is presented for the production of a Higgs boson in association with a single top quark, based on data collected in 2016 by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, which corresponds to an integrated luminosity of 35.9 fb(-1). The production cross section for this process is highly sensitive to the absolute values of the top quark Yukawa coupling, y(t); the Higgs boson coupling to vector bosons, g(HVV); and, uniquely, their relative sign. Analyses using multilepton signatures, targeting H -> WW, H -> tau tau, and H -> ZZ decay modes, and signatures with a single lepton and a b (b) over bar pair, targeting the H -> b (b) over bar decay, are combined with a reinterpretation of a measurement in the H -> gamma gamma channel to constrain y(t). For a standard model-like value of g(HVV), the data favor positive values of y(t) and exclude values of y(t) below about -0.9y(t)(SM).

In this issue of Neuron, Du et al. (2019) demonstrate that the bicistronic CACNA1A gene encodes a transcription factor alpha 1ACT, mutations in which are associated with SCA6, that controls expression of genes important for cerebellar Purkinje cell development and excitability. Reduction of alpha 1ACT in the adult is well tolerated, suggesting a potential new therapy for SCA6.

Spastin is a microtubule-severing AAA (ATPases associated with diverse cellular activities) protein needed for cell division and intracellular vesicle transport. Currently, we lack chemical inhibitors to probe spastin function in such dynamic cellular processes. To design a chemical inhibitor of spastin, we tested selected heterocyclic scaffolds against wild-type protein and constructs with engineered mutations in the nucleotide-binding site that do not substantially disrupt ATPase activity. These data, along with computational docking, guided improvements in compound potency and selectivity and led to spastazoline, a pyrazolyl-pyrrolopyrimidine-based cell-permeable probe for spastin. These studies also identified spastazoline-resistance-conferring point mutations in spastin. Spastazoline, along with the matched inhibitor-sensitive and inhibitor-resistant cell lines we generated, were used in parallel experiments to dissect spastin-specific phenotypes in dividing cells. Together, our findings suggest how chemical probes for AAA proteins, along with inhibitor resistance-conferring mutations, can be designed and used to dissect dynamic cellular processes.

The precise control of CRISPR-Cas9 activity is required for a number of genome engineering technologies. Here, we report a generalizable platform that provided the first synthetic small-molecule inhibitors of Streptococcus pyogenes Cas9 (SpCas9) that weigh <500 Da and are cell permeable, reversible, and stable under physiological conditions. We developed a suite of high-throughput assays for SpCas9 functions, including a primary screening assay for SpCas9 binding to the protospacer adjacent motif, and used these assays to screen a structurally diverse collection of natural-product-like small molecules to ultimately identify compounds that disrupt the SpCas9-DNA interaction. Using these synthetic anti-CRISPR small molecules, we demonstrated dose and temporal control of SpCas9 and catalytically impaired SpCas9 technologies, including transcription activation, and identified a pharmacophore for SpCas9 inhibition using structure-activity relationships. These studies establish a platform for rapidly identifying synthetic, miniature, cell-permeable, and reversible inhibitors against both SpCas9 and next-generation CRISPR-associated nucleases.

Associative learning of food cues that link location in space to food availability guides feeding behavior in mammals. However, the function of specific neurons that are elements of the higher-order, cognitive circuitry controlling feeding behavior is largely unexplored. Here, we report that hippocampal dopamine 2 receptor (hD2R) neurons are specifically activated by food and that both acute and chronic modulation of their activity reduces food intake in mice. Upstream projections from the lateral entorhinal cortex (LEC) to the hippocampus activate hD2R cells and can also decrease food intake. Finally, activation of hD2R neurons interferes with the encoding of a spatial memory linking food to a specific location via projections from the hippocampus to the septal area. Altogether these data describe a previously unidentified LEC > hippocampus > septal higher-order circuit that regulates feeding behavior.

Bacteria can readily generate mutations that prevent bacteriophage (phage) adsorption and thus make bacteria resistant to infections with these viruses. Nevertheless, the majority of bacteria carry complex innate and/or adaptive immune systems: restriction-modification (RM) and CRISPR-Cas, respectively. Both RM and CRISPR-Cas are commonly assumed to have evolved and be maintained to protect bacteria from succumbing to infections with lytic phage. Using mathematical models and computer simulations, we explore the conditions under which selection mediated by lytic phage will favour such complex innate and adaptive immune systems, as opposed to simple envelope resistance. The results of our analysis suggest that when populations of bacteria are confronted with lytic phage: (i) In the absence of immunity, resistance to even multiple bacteriophage species with independent receptors can evolve readily. (ii) RM immunity can benefit bacteria by preventing phage from invading established bacterial populations and particularly so when there are multiple bacteriophage species adsorbing to different receptors. (iii) Whether CRISPR-Cas immunity will prevail over envelope resistance depends critically on the number of steps in the coevolutionary arms race between the bacteria-acquiring spacers and the phage-generating CRISPR-escape mutants. We discuss the implications of these results in the context of the evolution and maintenance of RM and CRISPR-Cas and highlight fundamental questions that remain unanswered. This article is part of a discussion meeting issue 'The ecology and evolution of prokaryotic CRISPR-Cas adaptive immune systems'.